Story: Grasslands

Page 1 – Tussock grasslands

New Zealand’s native grasslands are dominated by tussocks
– grasses that have a clumping growth form, with stems
fanning up and outward from a central bunch.

This growth form helps grasses to survive. Much of the
plant is protected in a bunch of basal stems, unlike woody
plants, which have exposed and vulnerable growing stem tips.
Tussocks tolerate fire better than most woody plants.

In the past, farmers burnt off large areas of tussock and
tried to replace it with imported grasses, so they could
graze more animals. But many people’s attitudes have changed,
and grasslands are now valued as important native ecosystems.
Tussocks are also popular with gardeners.

Native grasses

New Zealand has around 190 native grass species. Native
tussocks belong to three genera: Chionochloa,
Poa and Festuca. Most of the 24 species of
Chionochloa have a tussock growth form – so do three
important Poa species and three Festuca
species.

Grass habitats

Grasses favour open areas. Very few grow under a closed
forest. A few grow on sand dunes or coastal cliffs, but they
do not form extensive grasslands.

Most New Zealand grasslands are tussocklands. Before
people arrived, there were also some low-growing sward
(carpet-like) grasslands – around 2% of the total grassland
area. These have been largely replaced by introduced grasses
for farming.

Extent of grasslands

The extent of native grasslands has varied in response to
the climate, and the frequency and intensity of fire. Over
the last 10,000 years (the Holocene period), grasslands
formed a mosaic with areas of woody vegetation in many parts
of New Zealand. The pattern varied according to altitude,
topography, slope, aspect and disturbance (including fire).
Grasslands mainly grew in areas that were colder or drier
than those which supported shrubland, woodland or forest.

Grasslands reached their greatest extent in the early
1800s, after Māori fires had burned much of the forest in the
drier regions, and before Europeans settled in New Zealand
and cleared land for farming. At that time, grasslands
probably covered about 31% of the mainland (around 83,700
square kilometres).

What is a tussock?

‘Scientifically speaking, a tussock is not actually a
single group of related plants but a growth habit – a
particular arrangement of stems and leaves which forms a
tuft of vegetation. The stems, or tillers from which the
leaves sprout are unusually tightly clustered.’1

Grasslands and animals

New Zealand’s grassland ecosystems developed in the
absence of grazing mammals. Birds and invertebrates were the
main browsers until European settlers brought grazing mammals
in the mid-1800s. Scientists still debate the extent to which
introduced herbivores have taken the place of native browsing
birds such as the now extinct moa.

Grasslands have a rich and diverse invertebrate fauna. As
specific groups of life forms evolve over millions of years,
this indicates the prolonged presence of grassland habitats
at all altitudes in New Zealand’s past. They also supported
many reptiles and birds.